1. Field of the Invention
The present invention relates to an apparatus and method for writing data to a phase-change random access memory (PRAM) by using writing power calculation and data inversion functions, and more particularly, to an apparatus and method for writing data which can minimize power consumption by calculating the power consumed while input original data or inverted data is written to a PRAM and storing the data that consumes less power.
This work was supported by the IT R&D program of MIC/IITA.[2005-S-072-02, Technology of a nano scale phase change data storage]
2. Description of the Related Art
A phase-change random access memory (PRAM) is a memory using a GST (Ge2Sb2Te5) material which has two different resistances according to the status of a memory cell. The PRAM should be in a set state which has low resistance in order to store data of “0” in the PRAM, and in order to put the PRAM in a set state, a set current pulse which enables set current to flow for a set period of time should be supplied to a phase change memory cell.
On the other hand, to store data of “1” in the PRAM, the PRAM should be in a reset state which has high resistance, and in order to put the PRAM in the reset state, a reset current pulse which enables reset current to flow for a reset period of time should be supplied to a phase change memory cell.
For a writing process to store data in the memory cell, the PRAM consumes a substantial amount of power since a large electric current flows through a phase change memory cell for a long period of time. On the other hand, a data reading process needs a small electric current which flows for a short period of time through a phase change memory cell, and therefore the power consumption for reading data is relatively smaller than that for writing data.
In the conventional art, the PRAM always performs the data writing process regardless of the value of the data stored in a memory cell. Also when the data is stored, data comprising several bits is stored in the PRAM as a word unit. Such a method of storing data is not efficient since the same bits may be repeatedly written, and thus the writing power may be unnecessarily consumed for writing data redundantly.